CartToSummaryMapper.cs

using AutoMapper;
using AutoMapper.Internal;
using MappingObjects.Models;

namespace MappingObjects.Mappers;

public static class CartToSummaryMapper
{
    public static MapperConfiguration GetMapperConfiguration()
    {
        MapperConfiguration config = new(cfg =>
        {
            cfg.Internal().MethodMappingEnabled = false;

            cfg.CreateMap<Cart, Summary>()
                .ForMember(dest => dest.FullName, 
                    opt => opt.MapFrom(src =>
                    string.Format("{0} {1}", src.Customer.FirstName, src.Customer.LastName)));
        });
        return config;
    }
}

OrderValidator.cs

using System.Data;
using FluentValidation.Models;

namespace FluentValidation.Validators;

public class OrderValidator: AbstractValidator<Order>
{
    public OrderValidator()
    {
        RuleFor(order => order.OrderId)
            .NotEmpty();
        RuleFor(order => order.CustomerName)
            .NotNull()
            .WithName("Name");
        RuleFor(order => order.CustomerName)
            .MinimumLength(5)
            .WithSeverity(Severity.Warning);
        RuleFor(order => order.CustomerEmail)
            .NotEmpty()
            .EmailAddress();
        RuleFor(order => order.CustomerLevel)
            .IsInEnum();
        When(order => order.CustomerLevel == CustomerLevel.Gold, () =>
        {
            RuleFor(order => order.Total)
                .LessThan(500);
            RuleFor(order => order.Total)
                .GreaterThan(1000);
        }).Otherwise(() =>
        {
            RuleFor(order => order.Total)
                .LessThan(1000);
        });
    }
}